Previous disclosures have discussed various methods of optimizing thin film filter set designs particularly in designing color filters compatible with detector fabrication processes. For example, previously disclosed thin film optimization methods involved coupling of certain pairs of layers between Cyan Magenta Yellow (“CMY”) or Red Green Blue (“RGB”) filter sets and optimization for performance (as disclosed, for example, U.S. provisional application Ser. No. 60/850,429, filed 10 Oct. 2006, entitled ELECTROMAGNETIC ENERGY DETECTION SYSTEM INCLUDING BURIED OPTICS).
TABLE 1Physical thickness (Angstroms)Differ-LayerMaterialCyanMagentaYellowenceMask #MediumPolyimide1UV SiN731.6731.6731.62BD 1036A914.8914.8914.83UV SiN1153.8529.5529.5624.354BD 1036A855.0855.0855.05UV SiN1004.91004.9397.6607.346BD 1036A883.2883.2883.27UV SiN1182.7540.5540.5642.238BD 1036A883.8883.8883.89UV SiN960.4960.4389.7570.7210BD 1036A854.7854.7854.711UV SiN1093.0591.2591.2501.81Substrate: PE-OX 11 KTotal thickness10518.08749.77571.6
TABLE 1 is a summary of an exemplary filter design for a CMY filter including a group of three filter designs. These examples of multilayer thin film filter designs, including first, second and third filter designs are designated in TABLE 1 as Cyan, Magenta, and Yellow, respectively, based on the associated single-color band pass optical response of each filter. Each filter design is provided as an ordered stack of layers such that each of the layers is designated in TABLE 1 as having a given physical thickness of a given material, as will be described immediately hereinafter.
A “Material” column in TABLE 1 specifies an ordered stack of an assortment of three different materials including, by way of example, polyimide, UV silicon nitride (“UV SiN”) and BLACK DIAMOND® (“BD”) 1036A. Layers 1-11 are designated in TABLE 1 as being arranged in a specific order of materials that is the same for all three filters, over a substrate of PE-OX 11 K. It is noted that the order of materials shown in TABLE 1 (and in subsequent tables including similar information) is given in the order encountered by electromagnetic energy incident thereon. That is, the order of materials is listed and numbered in a “Layer” column from top to bottom such that layer 1 of UV SiN corresponds to a final, or top, layer for the three physical filters, while layer 11 corresponds to the first layer deposited directly on the substrate during the actual fabrication of the filters.
In addition, to specifying an order of materials for all three of the filters, TABLE 1 designates a specific thickness for each selected layer of each filter. For example, layer 11 of the Cyan filter is specified in TABLE 1 as being composed of UV SiN and having a thickness of 1093.0 Angstroms, layer 11 of the Magenta filter is specified as being a 591.2 Angstrom thick layer of UV SiN, and layer 11 of the Yellow filter is specified as a 591.2 Angstrom layer of UV SiN. While the order of materials is the same for all three filters in TABLE 1, the thickness of a given layer of a given material may differ from one filter to another. The foregoing point is summarized, at least in part, in the “Difference” column of TABLE 1, which lists a number of differences in thickness between a corresponding number of pairs of layers that are distributed throughout the group of filters. For example, a thickness difference, having a value of 624.3 Angstroms, is identified in TABLE 1 between layer 3 of the Cyan filter and layer 3 of the Magenta filter. In addition, other thickness differences are identified in a number of pairs of layers that are distributed throughout the group of filters. For example, there are a number of thickness differences between the Cyan filter and the Yellow filter, including a thickness difference of 501.8 Angstroms between layer 11 of the Magenta filter and layer 11 of the Yellow filter.
TABLE 2DepositionThicknessEtch depthStep #DescriptionMaterial(Angstroms)(Angstroms)Mask#1Blanket depositionUV SiN501.82Spin coatPhotoresist3Masked exposure14Plasma etch501.85Remove photoresist6Blanket depositionUV SiN591.27Blanket depositionBD 1036A854.78Blanket depositionUV SiN570.79Spin coatPhotoresist10Masked exposure211Plasma etch570.712Remove photoresist13Blanket depositionUV SiN389.714Blanket depositionBD 1036A883.815Blanket depositionUV SiN642.216Spin coatPhotoresist17Masked exposure318Plasma etch642.219Remove photoresist20Blanket depositionUV SiN540.521Blanket depositionBD 1036A883.222Blanket depositionUV SiN607.323Spin coatPhotoresist24Masked exposure425Plasma etch607.326Remove photoresist27Blanket depositionUV SiN397.628Blanket depositionBD 1036A855.029Blanket depositionUV SiN624.330Spin coatPhotoresist31Masked exposure532Plasma etch624.333Remove photoresist34Blanket depositionUV SiN529.535Blanket depositionBD 1036A914.836Blanket depositionUV SiN731.6
Attention is now turned to TABLE 2, which summarizes an exemplary set of thin film fabrication processes required in fabricating the three-filter set described in relation to TABLE 1. These processes include a number of blanket deposition processes for specific materials that are designated in a “Material” column of TABLE 2. Each blanket deposition process is also specified as being deposited to a specific thickness as indicated in TABLE 2 by a “Thickness” column. The “Description” column of TABLE 2 further delineates a number of etching processes for removing a given thickness of material, the thickness being specified according to an “Etch depth” column. It is noted that a given etching process may require additional supporting process steps, in accordance with well-known thin film fabrication techniques that will be familiar to one having ordinary skill in the art and as indicated in the Description column of TABLE 2. For example, an etching process can include spin coating of photoresist, masked exposure, and removal of photoresist. It is recognized herein that a given etching step, combined with additional supporting process steps required for the given etching step, may together be regarded as encompassing a “recipe” for that given etching step. For example, steps 2-5 of TABLE 2 may be regarded as cooperating with one another to serve as a single recipe for etching 501.8 Angstroms of UV SiN. Additionally, a given deposition process, like an etching process, may itself be regarded as a recipe, and any given deposition requires a series of well-known steps that may depend on the details of a particular deposition system that may be employed to perform the given deposition.
TABLE 3UV SiN deposition recipesBD deposition recipesEtching recipes501.8 Å854.7 Å501.8 Å389.7 Å883.8 Å570.7 Å570.7 Å855.0 Å642.2 Å642.2 Å914.8 Å607.3 Å397.6 Å624.3 Å607.3 Å624.3 Å529.5 Å914.8 Å731.6 Å
In view of the foregoing description, a given set of filters may be produced by utilizing a number of recipes for deposition and etching of the various materials. An exemplary set of recipes is summarized in TABLE 3, which lists the various deposition and etching recipes in accordance with the fabrication process outlined in TABLE 2. First (i.e., leftmost) and second (i.e., center) columns of TABLE 3 lists a total number of fourteen deposition recipes required to perform the fabrication process of TABLE 2, each deposition recipe serving to deposit a specific thickness of one of UV SiN and BD. A third (i.e., rightmost) column in TABLE 3 itemizes the five etching recipes that are required to perform the fabrication process of TABLE 2. In the deposition and/or etching of each layer in a thin film filter, each combination of material and physical thickness may require the development of a recipe for that layer and, as summarized in TABLE 3, a total of 19 recipes are required for producing the CMY filter set of TABLE 1.
Turning now to the figures, wherein like components are indicated by like reference numbers throughout the various figures, attention is now directed to FIG. 1. It is noted that, while descriptive terminology such as, for example, top, bottom, right and left, may be used with respect to these descriptions, this terminology has been adopted with the intent of facilitating the reader's understanding and is not intended as being limiting. Further, the figures may not be drawn to scale for purposes of illustrative clarity. FIG. 1 shows a plot, generally indicated by reference number 6, illustrating the filter responses (i.e., transmission as a function of wavelength) for the Cyan, Magenta, and Yellow filters, respectively, as described above with reference to TABLES 1 and 2. A vertical axis 9 corresponds to percent transmission of electromagnetic energy (e.g., as light) through a given filter, and a horizontal axis 12 corresponds to a wavelength of the given electromagnetic energy. A first filter response 15 corresponds to the percent transmission through the Cyan filter for a range of wavelengths of the incident electromagnetic energy. A second response 18 corresponds to a filter response of the Magenta filter previously discussed with reference to TABLE 1. A third filter response 21 corresponds to a filter response of the Yellow filter of TABLE 1.
It is noted that the design of the various filters may be configured such that the filter responses 15, 18 and 21 may each satisfy a given preset criterion. As one example of a preset criterion, it will be readily appreciated by those skilled in the art that for a particular application, such as for use in an imaging system, each filter may be required to transmit a predetermined percentage of electromagnetic energy (e.g., light) at a given wavelength or over a given wavelength range.
Attention is now directed to FIG. 2 in conjunction with FIG. 1. FIG. 2 shows a plot, generally indicated by a reference number 26, illustrating the filter response of an RGB filter, which has been synthesized based on the CMY filter set of TABLE 1. While the plots of FIG. 1 each correspond to one and only one associated filter in TABLE 1, the plots of FIG. 2 each correspond to combinations of filters in TABLE 1, following standard conventions that are based upon well-known derivations that employ additive and subtractive relationships between CMY response and RGB response of the filter set. FIG. 2 has the same vertical axis 9 and horizontal axis 12 that are utilized in FIG. 1. A first filter response 27 corresponds to a first filter that is substantially transmissive with respect to a first range of wavelengths corresponding to the color Red. A second filter response 28 corresponds to a second filter that is substantially transmissive with respect to a second range of wavelengths corresponding to the color Green. Finally, a third filter response 31 corresponds to a third filter that is substantially transmissive over a third range of wavelengths corresponding to the color Blue. As one example, the three filter responses of FIG. 2 may be collectively referred to, in accordance with well-known conventions and terms of art, as a RGB filter set.
While the three-filter set described in association with TABLES 1-3 and FIGS. 1 and 2 provide adequate performance, the exemplary design requires nineteen distinct recipes in fabrication, each requiring fabrication and handling steps that may consequently add to the overall cost and reduce the overall yield of the filter set. Systems and methods disclosed herein overcome various disadvantages associated with current thin film filter designs and fabrication processes.